This invention relates to valving devices for oil field drilling systems and is particularly directed to an improvement in upper kelly cock valves. More specifically, this invention is related to an improvement in gate valves for use as upper kelly cock valves and will be described as such, however, this invention may also be used in any other application where there is a need for improved gate valves.
A kelly cock valve and its function in drilling operations has been described in a number of U.S. Pat. Nos. for example, in Kellner, U.S. Pat. No. 3,806,082, in Kubelka U.S. Pat. No. 3,887,161, in Winegeart et al U.S. Pat. No. 4,456,217, and in Winegeart U.S. Pat. No. 4,519,576. As pointed out in these patents, as part of the drilling assembly, a rotary swivel is supported by a traveling block in a derrick and is provided with means for conducting drilling fluids therethrough. In operation, the swivel is connected to a kelly cock valve through which the drilling fluids also flow, which, in turn, is connected to a kelly. The kelly extends to the floor of the drilling rig where it is engaged by a rotary table so that rotation may be imparted to the kelly and to the drill string.
The purpose the the kelly cock valve is to close the drilling assembly to the flow of fluid due to the fact that, frequently during drilling operations, a well may blowout reversing the flow of fluid. Since the kelly cock valve is normally at an elevated position in the drilling rig, closure of the valve required a derrick hand to climb up the drilling rig and manually close the valve. The time delay in closing the valve was such a problem that attempts were made to provide remote or automatic controls on such valves, but such attempts met with only limited success.
One reason for such limited success is that, historically, the kelly cock valves have been ball valves and the attempts to provide ball valves with automatic or remotely operated closing mechanisms are simply add-ons to an existing valve design. Thus, the ball valves, having been designed for manual operation, are difficult to operate remotely or automatically. The add-ons are usually large and cumbersome, subject to frequent breakdown, and generally unreliable. Also, to repair, either the valve itself or the remote/automatic control mechanism, the entire valve assembly has to be removed from the drilling system and, if this occurs during drilling operations, the time lost is quite expensive.
This invention, on the other hand, is intended to replace the ball valve as a kelly cock valve with a gate valve having the following advantages:
smaller in overall envelope size,
simpler in design,
more dependable in service, and
capable of being disassembled for repair without
removal of the entire valve.
Thus, this invention, being a gate valve, is intended as a replacement for existing kelly cock valves of the ball valve type.